任何人都可以帮助我解决我认为很简单的JPA问题。我正在尝试在我的JPA持久性框架中编写通用懒负载管理器,因此更高的层可以访问懒惰的数据,而无需处理细节。
我有一个懒惰的负载管理器:
public class JpaLazyLoader extends AbstractJpaDAO<Void> implements LazyLoader
{
public JpaLazyLoader()
{
super( void.class );
}
@Transactional(readOnly=true)
public <T,E> T get( ILazyGetter<T,E> p_getter ) throws Exception {
// reattach the object to the session
E l_entity = getEntityManager().merge( p_getter.getEntity() );
// return the getter data
return p_getter.get( l_entity );
}
}
懒惰的Getter就是这样:
public interface ILazyGetter<T,E> extends Serializable
{
public E getEntity();
public T get( E p_entity ) throws Exception;
}
的想法是它将像这样使用:
return m_lazyLoader.get( new ILazyGetter<Collection<Child>, Parent>() {
private static final long serialVersionUID = 1L;
public Parent getEntity() {
return getValue(); // get the parent object from somewhere
}
public Collection<Child> get( Parent p_entity ) throws Exception {
// children are a lazy-loaded Set<Child>
return p_entity.getChildren();
}
} );
父母的注释是这样的:
@Entity(name="parent")
public class Parent implements Serializable {
private static final long serialVersionUID = 1L;
....
@Id
@Column(name="id")
@GeneratedValue(strategy=GenerationType.AUTO)
protected Long id;
@OneToMany
@JoinTable
(
name="parent_child_associations",
joinColumns={ @JoinColumn(name="parent_id", referencedColumnName="id") },
inverseJoinColumns={ @JoinColumn(name="child_id", referencedColumnName="id", unique=true) }
)
protected Set<Child> children;
}
将父对象加载到不同的交易中,然后分离。我希望将父母重新安排到另一个会话( @transactional位),但我无法正常工作是一件琐碎的事情。我尝试过乐观/悲观/无锁定之前和之后,但似乎没有锁定。
org.hibernate.LazyInitializationException: failed to lazily initialize a collection of role: test.Parent.children, could not initialize proxy - no Session
at org.hibernate.collection.internal.AbstractPersistentCollection.throwLazyInitializationException(AbstractPersistentCollection.java:566)
at org.hibernate.collection.internal.AbstractPersistentCollection.withTemporarySessionIfNeeded(AbstractPersistentCollection.java:186)
at org.hibernate.collection.internal.AbstractPersistentCollection.initialize(AbstractPersistentCollection.java:545)
at org.hibernate.collection.internal.AbstractPersistentCollection.read(AbstractPersistentCollection.java:124)
at org.hibernate.collection.internal.PersistentSet.iterator(PersistentSet.java:180)
这只是错误的方式吗?如果是这样,"正确"的方式是什么?如果没有,我在做什么错?
感谢您的任何帮助
好吧,多亏了安德烈(Andre),我才能使用。
我根本没有初始化收集对象,而是在调用parent.getChildren(),它只是返回代理对象而不是强制提取。
以下更新的GET方法适用于有类似需求的任何人:
@Transactional(readOnly=true)
public <T,E> T get( ILazyGetter<T,E> p_getter ) throws Exception {
// reattach the object to the session
E l_entity = getEntityManager().merge( p_getter.getEntity() );
T l_lazyData = p_getter.get( l_entity );
// Just getting the data doesn't necessarily initialize it -
// explicitly initialize it depending on the data type.
intializeEntity( l_lazyData );
// return the getter data
return l_lazyData;
}
/**
* Attempt to initialize the entity so it is fully lazy loaded while in the transaction
* @param p_entity
*/
protected void intializeEntity( Object p_entity ) {
if( p_entity != null && p_entity instanceof Collection ) {
Collection<?> l_entity = (Collection<?>)p_entity;
l_entity.size(); // force the collection to load
}
}